Wheel alignment is a well-known motor vehicle characteristic that has a substantial impact on handling and maneuverability of a motor vehicles. In particular, parameters of toe (toe-in, toe-out) caster and camber all must be within certain specifications in order to maintain accurate tracking and steerability of the vehicle without excessive tire wear. Unfortunately, systems for setting alignment as well as systems determining data for recording and analysis of alignment characteristics are often difficult and complicated to use. In addition, they do not permit audit testing for compliance of production line output with the production line standards for such characteristics. Moreover, many of the setting systems influence or affect the alignment and the results of the tests, and may therefore indicate a particular vehicle system is within tolerance although it is outside the allowable standards. Moreover, the existing measuring gauges do not permit an audit of every automobile passing through a production line, as the time and labor required permit only limited sampling of selected units in a production run.
To improve production quality and maintaining high compliance with a predetermined level of standard deviation, automotive companies have been forced to monitor only portions of production. For example, the previously known systems, for example, Hunter Model No. C-111 wheel alignment system, includes a device mechanically attached to each wheel to establish whether the caster, camber and toe-in are aligned within a predetermined tolerance range. Nevertheless, the requirement for installation of the devices on portions of the vehicles substantially slows the monitoring of the particular vehicle's alignment. As a result, the test procedure is limited to off-line testing of only a selected few of the vehicles run during a production period. Moreover, the previously known Hunter system is subject to the proper installation of the device by the machine operator. Moreover, the laborious and time-consuming nature of the test does not render it applicable to testing for each vehicle on the production line. As a result, while production may be running at 60-90 vehicles per hour, the Hunter monitoring is useful in monitoring only about 1 or 2 production units per hour.
Other recent attempts to monitor the quality of vehicles during production for wheel alignment parameters was in a desired tolerance level include an Anzen auditing machine called G-SWAT that aligns itself with the vehicle by means of a pantograph. A Fori measuring system has a pivoting hitch for addressing the motor vehicle. Nevertheless, it will still be understood that these systems, that are four or five times faster than the previously known Hunter system because they use automated engagement of the mechanical devices on vehicle wheels, still suffer disadvantages discussed for the baseline Hunter system. The mechanically contacting devices require a skilled operator to use, may interfere with the alignment being sensed, and do not match the speed of production.
Another improved apparatus for aligning vehicle wheels is disclosed in U.S. Pat. Nos. 4,745,469 and 4,899,218. The system avoids the need for physical contact with the vehicle by using sensors that are self-contained, intelligent machine vision camera and illumination systems that include a laser source projecting a plane of light onto the wheel structure. The camera is mounted at a perspective angle relative to the axis of the projected light plane to produce image signals representing the contour as viewed from the perspective angle. The camera does not require the sensor to be mounted for displacement relative to the wheel. The wheel position information can be combined with similarly measured data defining a vehicle centerline or other references so that the system generates a display on a video monitor to guide an operator in adjusting the wheel alignment. Nevertheless, the immediate video feedback to the worker aligning the vehicle or even an immediate printout of alignment settings does not provide a system for monitoring the statistical variation throughout the entire production line or permit the immediate feedback to on-line or off-line production stations involved in setting the wheel alignment.